The present invention relates to torque wrenches. More particularly, it relates to such torque wrenches which has an engaging unit which engages a threaded connector and is turned so as to turn the threaded connector for tightening or loosening, and a fluid-operated drive unit including a cylinder and a piston movable in the cylinder and acting upon the engaging unit to turn the latter.
Torque wrenches of the above mentioned general type are widely known in the art.
The torque output of fluid-operated torque wrenches is based on the torque capacity of the engaging unit which can include for example a square drive, or in other words a square projection to which standard impact sockets can be attached. For example, a 1 inch square drive cannot take more than 3,100 ft./lbs since a torque higher than this would break off the square drive. A 1.5 inch square drive cannot take more than 12,000 ft./lbs. Therefore the tools are designed so that the maximum torque output at maximum pressure does not exceed the maximum torque capacity of a square drive. It is therefore desirable to provide such a torque wrench in which the maximum torque output can be adjusted to the maximum torque capacity of a respective square drive, in a simple, convenient and fool-proof manner, since an error in selecting the maximum torque output can lead to destruction of the square drive.